If the plastic is exposed to open flame or enough heat, it will burn. Most people are using LED tea candles for their candle holders, but here is a link to one I designed in WSF that works just fine with regular tea candles. It has been in use for about a year now with no trouble. It works because no plastic is exposed to the rising hot air. I also sprayed 6 coats of clear acrylic on to seal it, so that may (or may not) increase heat resistance.